PROCESS FOR THE MANUFACTURE OF beta -ACETOXYPIVALIC ALDEHYDE

ABSTRACT

Process for the manufacture of Beta -acetoxypivalic aldehyde by the dosed addition of Beta -hydroxypivalic aldehyde and/or its dimer in an acetic acid solution to a boiling mixture of acetic acid, an entrainer and an acid catalyst at a rate which corresponds to the speed of formation of reaction water.

United States Patent Ar e Dec. 12 1972 PROQESS FOR THE MANUFACTURE [58]Field of Search ..260/494 OF B-ACETOXYPKVALIC ALDEHYDE [75] Inventor:Hans-Jurgen Arpe, Fischbach/Tau- [56] Rem-em Cited nus, Germany UNITEDSTATES PATENTS [73] Assignee: Farbwerke lloechst Aktien- 488gesellschalt vormals Meister Lucius 325L876 5/1966 Moflock 26w g rgggFrankfurt am Primary ExaminerVivian Garner y AttorneyCurtis, Morris &Safford [22] Filed: Aug; 6, 1970 21 Appl. No.: 61,854 [571' ABSTRACTProcess for the manufacture of B-acetoxypivalic al- 30 ForeignApplication Priority Dam dehyde by the dosed addition ofB-hydroxypivalic aldehyde and/or its dimer in an acetic acid solution to21 Aug. 13,1969 Germany ..P 19 41 184.8 boiling mixture of acetic acid,an entrainer and an acid catalyst at a rate which corresponds to thespeed [52] US. Cl. ..260/494, 260/340.7, 260/49 l of formation ofreaction water 260/496 [51] Int. Cl ..C07c 67/00 3 Claims, No DrawingsPROCESS FOR THE MANUFACTURE OF [3- ACIE'HUXYPBVALIC ALDEHYDE The presentinvention relates to a process for the manufacture of fi-acetoxypivalicaldehyde.

It has been proposed to manufacture B-acetoxypivalic aldehyde of thefollowing formula cnrp-o cnkoto iinl ono In us. Pat. No. 3,251,876 amethod is described for the manufacture of B-acetoxypivalic aldehyde byheat ing B-hydroxypivalic aldehyde with a mixture of acetic acid andbenzene in the presence of mineral acids or ptoluenesulfonic acid withthe separation of water in a reflux condenser. After distilling off thebenzene and the excess amount of acetic acid, the acetoxy aldehyde isobtained in pure form by distillation under reduced pressure. Thisprocess, carried out as a single-pot process, has the disadvantage thatthe sensitive hydroxypivalic aldehyde is exposed to the refluxtemperature and the acid catalyst during the whole reaction time.

Japanese Pat No. 29,923/68 describes the manufacture offl-acetoxypivalic aldehyde by reaction of B- hydroxypivalic aldehyde orits dimer with acetic acid at temperatures above 80C in the absence of acatalyst. The said process avoids the detrimental influence of an acidcatalyst, but uses a considerably prolonged reaction time so that thesensitive aldehyde is exposed to the detrimental action of thetemperature to an increased degree.

The uncertainty how to choose the appropriate acetylation agent, forexample, isopropenyl acetate, acetic acid or acetanhydride, and theappropriate catalyst, for example, mineral acids or p-toluenesulfonicacid, or whether to work in the absence of any catalyst, is due to thechemical behavior of the starting substance B-hydroxypivalic aldehydewhich is present in a crystalline form as the dimer having the abovedioxane structure. By reacting, for example, the dimer with aceticanhydride in pyridine, the diacetate of the dimer is obtained (cf.Liebigs Ann. Chem., 627,96 (1959)). When the dimeric form ofB-hydroxypivalic aldehyde is reacted in the presence of a mineral acid,for example hydrochloric acid, the dimer has a tendency to split offwater and form a tetramer, i.e. tetraldane. From this follows that theacetylation should not be carried out in an alkaline or strongly acidmedium.

It has furthermore been known that B-hydroxypivalic aldehyde is veryunstable thermally and is either split into formaldehyde andisobutyraldehyde with realdolization or converted to thehydroxyneopentylic ester of B-hydroxypivalic acid withdisproportionation of the aldehyde group. Also for this reasonhydroxypivalic aldehyde puts special demands on the acetylation process.

Now 1 have found that the above side reactions can be substantiallyavoided and optimum yields of B- acetoxypivalic aldehyde can be obtainedby choosing an appropriate catalyst and adding the dissolved B-hydroxypivalic aldehyde to a mixture of acetic acid and benzene drop bydrop gradually as it is reacted to ,8- acetoxypivalic aldehyde,

The process of the invention for the manufacture of B-acetoxypivalicaldehyde by reaction of B-hydroxypivalic aldehyde and/or its dimer withacetic acid in the presence of an acid catalyst and an entrainer for thewater comprises adding B-hydroxypivalic aldehyde and/or its dimer in anacetic acid solution to a boiling mixture consisting of acetic acid, anentrainer and an acid catalyst at a rate corresponding to the speed offormation of water.

in detail the process of the invention is performed such that theesterification is carried out with an excess amount of acetic acid of 2to 8 times, preferably 4 to 6 times, the theoretical amount, using halfthe amount of the acetic acid used, together with a part of theentrainer serving to eliminate the water, for dissolving thehydroxyaldehyde and/or its dimer. As entrainer there may be usedsubstances forming an azeotropic mixture with water, for example,methylene chloride, chloroform, trichlorethylene, carbon tetrachloride,and preferably cyclohexane or benzene. The other half of the acetic acidis placed together with the remaining amount of entrainer and the acidcatalyst in the apparatus which is provided. with a water separator.

When the solution of B-hydroxypivalic aldehyde is added dropwise to theboiling mixture of acetic acid, entrainer and catalyst, esterificationsets in immediately, as can be recognized by the separation of water, inspite of the initially very small concentration of aldehyde, this beingsurprising. Thus the sensitive hydroxyaldehyde is converted to stableacetoxyaldehyde and no longer exposed to the action of the temperatureand the catalyst. The rate of addition of hydroxyaldehyde is increaseduntil it corresponds to the rate of elimination of the theoreticalamount of water (in the form of a diluted acetic acid). By proceeding inthis manner, the residence time of the B- hydroxypivalic aldehyde in thereaction medium is only short so that the ,B-hydroxypivalie aldehydecannot enter into side reactions.

When working in the absence of an acid catalyst, for example, a mineralacid, an acid ion exchanger or an organic acid, for examplep-toluenesulfonic acid, the esterification proceeds considerably moreslowly and thermally initiated side reactions take place.

Of the above acid catalysts, p-toluenesulfonic acid is preferably used.The latter may be used in an amount within the range of from 0.01 to 1mol percent, preferably 0.1 mol percent, calculated on the B-hydroxypivalic aldehyde. When, instead of ptoluenesulfonic acid, amineral acid for example sulfuric acid, is used in the sameconcentrations, no 0ptimum yields of acetoxypivalic aldehyde can beobtained, because relatively large amounts of higher boiling productsare formed, which is obviously due to the above mentionedtetramerization.

When, instead of the dosed addition in accordance with the inventionwhich is synchronous with the speed of reaction, a single pot process isused in which all the reaction components as well as the catalyst andthe entrainer for the water are present in the reaction vessel from thebeginning, low boiling and high boiling secondary products are formed atthe expense of B-acetoxypivalic aldehyde.

After the theoretical amount of water has been separated, the entrainerand the acetic acid in excess are distilled off, and theB-acetoxypivalic aldehyde is distilled under reduced pressure. The yieldis about 97 percent of the theoretical.

. B-Acetoxypivalic aldehyde is an important intermediate for themanufacture of pivalolactone which is the starting product forpolypivalolactone, a polyester which is used as thermoplastic and forthe manufacture of fibers.

The following examples serve to illustrate the invention.

EXAMPLEI Two hundred fifty-four grams B-hydroxypivalic aldehyde in theform of the dimer thereof were dissolved at room temperature in amixture of 300 grams acetic acid and 500 milliliters benzene. Theresulting solution was added dropwise in the course of 6 hours to aboiling solution of grams p-toluenesulfonic acid in 300 grams aceticacid and 500 milliliters benzene. The water which was formed was removedin the form of diluted acetic acid through a water separator. After thattime, the separation of water was terminated and the benzene and theacetic acid in excess were distilled off under atmospheric pressure. Asthis mixture was used again for the esterification after the consumedacetic acid had been replaced, the small amount of [3- acetoxypivalicaldehyde which distilled over azeotropically could also be returned. Theresidue was subjected to a fractional distillation under a pressure ofmillimeters of mercury. There were obtained 347 grams 96.6 mol percentB-acetoxypivalic aldehyde having a boiling point b.p. C.

EXAMPLEZ By using, instead of p-toluenesulfonic acid, 0.5 milliliterconcentrated sulfuric acid as catalyst, while otherwise proceeding underthe same conditions as those described in Example 1, the yield ofB-acetoxypivalic aldehyde was reduced to 76.0 mol percent.

EXAMPLEB When proceeding under the conditions of Example 1, but using,instead of the method of dropwise addition, a single pot process inwhich the total amount of reactants was simultaneously present, a yieldof only 81.6 mol percent B-acetoxypivalic aldehyde was obtained.

What is claimed is:

1. In a process for the manufacture of B-acetoxypivalic aldehyde byreaction of B-hydroxypivalic aldehyde or its dimer or mixtures thereofwith acetic acid in the presence of an acid catalyst and an entrainerfor water, the improvement which comprises adding B- hydrox pivalicaldehyde or its dimer or mixtures thereo m an acetic solution to aboiling mixture consisting of acetic acid, the total amount of which is2 to 8 times the theoretical amount, an entrainer selected from thegroup consisting of benzene and cyclohexane, and p-toluenesulfonic acidas catalyst at a rate corresponding to the speed of formation of waterof reaction.

2. The process of claim 1 wherein p-toluenesulfonic acid is used in anamount within the range of from 0.01 to 1 mol percent, calculated on theB-hydroxypivalic aldehyde.

3. The process of claim 1 wherein p-toluenesulfonic acid is used in anamount of 0.1 mol percent, calculated on the B-hydroxypivalic aldehyde.

1. In a process for the manufacture of Beta -acetoxypivalic aldehyde by reaction of Beta -hydroxypivalic aldehyde or its dimer or mixtures thereof with acetic acid in the presence of an acid catalyst and an entrainer for water, the improvement which comprises adding Beta -hydroxypivalic aldehyde or its dimer or mixtures thereof in an acetic solution to a boiling mixture consisting of acetic acid, the total amount of which is 2 to 8 times the theoretical amount, an entrainer selected from the group consisting of benzene and cyclohexane, and p-toluenesulfonic acid as catalyst at a rate corresponding to the speed of formation of water of reaction.
 2. The process of claim 1 wherein p-toluenesulfonic acid is used in an amount within the range of from 0.01 to 1 mol percent, calculated on the Beta -hydroxypivalic aldehyde. 